Rotary cone drill bits are primarily used in open pit mining and typically terminate in a structure that generally includes three lugs. A cone shaped bit including a plurality of cutting elements is arranged on each lug. The three cones are arranged such that they are angled toward a central point. A drilling fluid is used to evacuate drilled material from a hole as the bit drills into the material. The drilling fluid also cools and cleans bearing structures described below. When drilling with a rotary cone bit, the drill may be moved frequently. Air is typically used as the drilling fluid to increase the portability of the drilling apparatus.
FIG. 1 illustrates an example of a typical rotary bit in an upright position. The structure includes a central shaft 1. The shaft terminates with three lugs 3, 5, 7. A cone 9, 11, 13 is installed on each lug. FIG. 2 illustrates the structure shown in FIG. 1 such that a central axis of one of the cones is horizontal. FIG. 3 illustrates the structure shown in FIG. 2. FIG. 4 illustrates the view shown in FIG. 3 with only one lug shown.
FIG. 6 illustrates one of the lugs with the cone removed. To permit the cone to rotate on the lug, each lug includes a plurality of bearings and rollers. The lug and the cone include a plurality of races on which the bearings and rollers ride. This example of lug and bearing components includes a plurality of small rollers 17, a plurality of ball bearings 19 and a plurality of large rollers 21.
FIG. 7 illustrates an interior view of the cone. The cone includes races upon which the bearings and rollers ride when the bit is in use. This example of the cone includes a small roller race 23, a ball bearing race 25, and large roller race 27. The small rollers and small roller race may be referred to as an inner bearing. The large rollers and large roller race may be referred to as an outer bearing.
FIG. 8 illustrates the lug with the cone removed. As can be seen in FIG. 8, the lug includes a small roller race 29, a ball bearing race 31 and a large roller race 33. The bearings and rollers in place on the races is shown in FIG. 6.
The roller and bearing races are bounded and partially formed by flanges in the lug. Along these lines, small roller race 29 is bordered by pin flange 47 and thrust flange 49. Bearing race 31 is formed by thrust flange 49 and large roller race flange 51. The large roller race is bounded and formed by the large roller race flange 51 and the base flange 53. The diameter, thickness and contour of these flanges may vary depending upon the application and rollers and bearings being utilized.
To cool and facilitate removal of drilled material from the bearing cavity, the lug includes a plurality of passages extending therethrough. The passages direct fluid, typically air, from a central passage 15 in the shaft to the space between the lug and the cone as well as out of the end of the cone.
FIG. 9 illustrates a cross-sectional view of a lug with the cone attached. According to this example, the lug includes a long air hole, which feeds fluid from the shaft into the other passages in the lug and cone. The long air hole 35 feeds a plurality of additional passages 57 and 39 that branch off of the long air hole. Fluid, such as air, exits the long air hole and/or passages through various openings as described below.
FIG. 9 also illustrates the small rollers 17 and races 23, 29, ball bearings 19 and races 25, 31, and large rollers 21 and races 27 and 33. The lug and cone are formed such that spaces between the cone and lug will permit the fluid to pass between the lug and the cone. Such passages can include a secondary exhaust slot 67 (FIG. 8). The gap between the cone and lug at the perimeter may generate an “air curtain” that helps to prevent drilling debris from entering the space between the cone and the lug.
As also shown in FIG. 9, a ball plug 43 may be arranged in the flow passage 37. The ball plug retains the ball bearings after they are introduced into the bit assembly. Along these lines, the ball bearings help to retain the cone on the lug. The cone is typically assembled with the rollers already on the lug. The ball bearings may then be loaded through the flow passage 37 and out of ball loading hole 63 into the space between the lug and the cone where they ride on the ball race. The ball bearings lock the cone onto the lug. After the ball bearings are inserted, the ball plug 43 is inserted into ball loading hole 37 and welded into place to retain the ball bearings in the ball race and the cone on the lug.
Additionally, a thrust button may be installed or a weld added to the lug and cone and be arranged at the end of flow passage 39. The thrust buttons or welded flanges in the lug and cone form one of the two axial bearings at the end of passageway 39. The other and main axial bearing is the thrust flanges 49 for the lug and 25 for the cone.
Fluid flowing through the various flow passages can exit the lug from various passages in the lug. For example, FIG. 8 illustrates various openings through which the fluid may pass. The openings can include a centerline air hole 45 at the end of flow passage 39. Fluid flowing through the centerline air hole 45 can pass through a hole in the lug thrust button and may also be directed through slots 55 in the pin flange 47.
Fluid may exit the lug through thrust flange air holes 57 in the surface of the flange that faces the small rollers. The thrust flange may include a region of reduced thickness 59, or thrust flange mill slots (TFMS), in the vicinity of the thrust flange air holes to facilitate air flow out of the thrust flange air holes. To further direct fluid flow from the thrust flange air holes, the region of increased flange cut depth may be bordered by slot edges 61 in the surface of the thrust flange. Fluid may exit from flow passage 37 shown in FIG. 9 out of ball loading hole 63 shown in FIG. 8.
Fluid may also pass through a primary exhaust slot 65 and a secondary exhaust slot 67 arranged on the lug in the vicinity of the base of the cone. Air may pass through the primary exhaust slot and the secondary exhaust slot.
During drilling operations, the drill bit assembly shown in FIGS. 1-5 rotates in a clockwise direction from the perspective looking down the hole. The lowest parts of the cones shown in FIGS. 1 and 5 form the load bearing surfaces of the bit, with the lower leading edge 69 of the bit shown in FIGS. 1, 2, and 5.
When air is used as a drilling fluid, the air pressure may vary depending upon the application. According to one example, a minimum pressure of 45 psi or 3.1 bar is utilized. This can help to ensure delivery of sufficient air to the bearings and rollers to make them functional. The pressure can vary depending upon the specific drill rig and compressor being utilized, the operating altitude, as well as other factors. The size of the flow passages, including the nozzles, can vary to produce the desired pressure, depending upon the pressure affecting variables. It is desirable for the pressure to remain below a level at which compressors providing the air could modulate, which can reduce the overall output.